You have found the following ages (in years) of 5 snakes. Those snakes were randomly selected from the 35 snakes at your local zoo: $ 22,\enspace 10,\enspace 22,\enspace 20,\enspace 8$ Based on your sample, what is the average age of the snakes? What is the standard deviation? You may round your answers to the nearest tenth.
Answer: Because we only have data for a small sample of the 35 snakes, we are only able to estimate the population mean and standard deviation by finding the sample mean $({\overline{x}})$ and sample standard deviation $({s})$ To find the sample mean , add up the values of all $5$ samples and divide by $5$ $ {\overline{x}} = \dfrac{\sum\limits_{i=1}^{{n}} x_i}{{n}} = \dfrac{\sum\limits_{i=1}^{{5}} x_i}{{5}} $ $ {\overline{x}} = \dfrac{22 + 10 + 22 + 20 + 8}{{5}} = {16.4\text{ years old}} $ Find the squared deviations from the mean for each sample. Since we don't know the population mean, estimate the mean by using the sample mean we just calculated {31.36} + {40.96} + {31.36} + {12.96} + {70.56}} {{5 - 1}} $ {s^2} = \dfrac{{187.2}}{{4}} = {46.8\text{ years}^2} $ As you might guess from the notation, the sample standard deviation $({s})$ is found by taking the square root of the sample variance $({s^2})$ ${s} = \sqrt{{s^2}}$ $ {s} = \sqrt{{46.8\text{ years}^2}} = {6.8\text{ years}} $ We can estimate that the average snake at the zoo is 16.4 years old. There is also a standard deviation of 6.8 years.